In earlier studies we showed that norepinephrine, acting as an alpha adrenergic antagonist, inhibited the water permeability response of the toad urinary bladder to vasopressin and to theophylline, but not that to cyclic AMP, presumably because norepinephrine inhibited adenylate cyclase activity. In this study we are examining a second and possibly related effect of norepinephrine, increased responsiveness to vasopressin and theophylline after withdrawal of norepinephrine from the incubation solution. Experiments will be performed to identify the type (alpha vs. beta) of adrenergic activity involved, and the site of the effect (adenylate cyclase, cyclic nucleotide phosphodiesterase, etc.).